The Multi-Busbar Design: an · PDF file4th thMetallization Workshop, May 8 2013, Konstanz S. Braun The Multi-Busbar Design: an Overview Stefan Braun1,Giso Hahn1 Robin Nissler2, Christoph

4th Metallization Workshop, May 8th 2013, Konstanz S. Braun

The Multi-Busbar Design: an Overview

Stefan Braun1, Giso Hahn1

Robin Nissler2, Christoph Pönisch2,

Dirk Habermann2

Universität Konstanz1

www.uni-konstanz.de/photovoltaics

Gebr. Schmid GmbH2


Optimized Solar Cell Design for Module Integration*

Motivation

*S. Braun et al., “Solar Cell Improvement by Using a Multi-Busbar Design as Front Electrode”, Energy Procedia 21, 227-233 (2012)

1

Multi-Busbar Solar Cell

Ag consumption Module Solar cell optimization

+ =


Outline

• Motivation

• Cell Concepts

- Differences between 3-busbar and multi-busbar solar cell

• Simulation

- Advantages of multi-busbar design on cell- and module-level

• Results of Experiment

- Solar cells & one cell modules

• Summary

2


Cell Concepts

3

Alkaline textured

SiNx:H layer

Screen printed fingers

Full area Al BSF

SE Solar Cell (6 inch Cz)


Cell Concepts

3-Busbar Multi-Busbar

3

3 Busbars Round Sn coated Cu wires

Alkaline textured

SiNx:H layer

Screen printed fingers

Full area Al BSF

SE Solar Cell (6 inch Cz)


Extraction IV Parameters

Starting Point

2-diode model simulation

4


Extraction IV Parameters

Starting Point

2-diode model simulation

4

jsc [mA/cm2] Voc [mV] FF [%] η [%]

37.63 638.7 79.78 19.17

*B. Tjahjono et al.,”Optimizing selective emitter technology in one year of full scale production”, Proc. 26th EUPVSEC Hamburg, p. 901-905

j01 [fA/cm2] j02 [nA/cm2] rp [cm2] rs [cm2] jph [mA/cm2]

538 17 10000 0.433 40.5**

**without shading

Selective Emitter

reference cell*

Extracted

parameters


Simulation

5

Adding busbars to cell structure

Busbar width 1.4 mm

3 4 5 6 7 8 9 1018.0

18.2

18.4

18.6

18.8

19.0

19.2

19.4

[

%]

Busbars

Cell

Stringed

Stringed opt.

How many busbars do we need?

IV setup

Shading dominates

drop

IV setup


Simulation

6


Busbar width 1.4 mm

Height of rectangular tabbing 200 µm

Shading dominates

drop

3 4 5 6 7 8 9 1018.0

18.2

18.4

18.6

18.8

19.0

19.2

19.4

[

%]

Busbars

Cell

Stringed

Stringed opt.

• drop due to stringing

• Additional Rs by tabbing

• IV measurement does not represent module

..performance

Stringed front side


Simulation

7

Busbar width variable


Rs reduction dominates

η gain


3 4 5 6 7 8 9 1018.0

18.2

18.4

18.6

18.8

19.0

19.2

19.4

[

%]

Busbars

Cell

Stringed

Stringed opt.

Stringed front side


Simulation

8


Busbar width variable


3 4 5 6 7 8 9 1018.0

18.2

18.4

18.6

18.8

19.0

19.2

19.4

[

%]

Busbars

Cell

Stringed

Stringed opt.0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Bu

sba

r w

idth

[m

m]

Stringed front side

Rs reduction dominates

η gain


String Geometry

Tabbing

Reflection on string

Effectively shaded area: ~100%

Reflection on wire


Wire

9


Tabbing

Total reflection on glass


Wire



10

String Geometry


String Geometry

Tabbing

Partial reflection on glass

Effectively shaded area: 30%*

Wire



11

*A.W. Blakers, "Shading losses of solar-cell metal grids“, Journal of Applied Physics, vol. 71, p. 5237, 1992


Finger Design

12

Series resistance rs of

finger grid:

rs ~ L2

rs 3BB 25 times higher

with same grid structure

L = 25 mm L = 5 mm

3-Busbar, 6 inch Multi-Busbar (15 wires), 6 inch


10 20 30 40 50 60 70 80 900.0

0.2

0.4

0.6

0.8

1.0

r s [

cm

2]

Finger width [µm]

3 Busbars

15 Wires

Finger Design

Finger spacing constant (2 mm) Aspect ratio height/width = 0.5

Gaussian shaped fingers

13

IV setup

L = 25 mm L = 5 mm



10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

r s [

cm

2]

Finger width [µm]

3 Busbars

15 Wires

0.0

0.4

0.8

1.2

1.6

2.0

2.4

Fin

ge

r sp

acin

g [

mm

]

Finger Design

Finger spacing variable Aspect ratio height/width = 0.5

Gaussian shaped fingers

14

IV setup

L = 25 mm L = 5 mm



10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

r s [

cm

2]

Finger width [µm]

3 Busbars

15 Wires

18.8

19.0

19.2

19.4

19.6

19.8

20.0

[%

]

IV setup

Ag Consumption & Efficiency

15

Finger width η

3 Busbars 50 µm 19.3%

15 Wires 17 µm 19.7%


10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

r s [

cm

2]

Finger width [µm]

3 Busbars

15 Wires

18.8

19.0

19.2

19.4

19.6

19.8

20.0

[%

]

IV setup

10 20 30 40 50 60 70 80 900.0

0.1

0.2

0.3

0.4

0.5

0.6

r s [

cm

2]

Finger width [µm]

3 Busbars

15 Wires

0

30

60

90

120

150

180

Ag

pa

ste

[m

g]

15

Finger width η Ag consumption

3 Busbars 50 µm 19.3% 108 mg

15 Wires 17 µm 19.7% 6.7 mg

Ag Consumption & Efficiency

IV setup


Aluminium Rear Side

• Pad size 4 mm x 0.5 mm

• 15 round Cu wires

• Rsheet Al = 10 m/sq. ~ 18 µm

How many Ag Pads on Al Rear Side?

16

?

continuous

6 5 4 3 2 Pads on

unit cell

Al rear side


220 240 260 280 3000.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

r s [

cm

2]

Wire diameter [µm]

2 Pads

3 Pads

4 Pads

5 Pads

6 Pads

Continuous

Aluminium Rear Side

Number of pads

depends on wire

diameter


17

Stringed rear side

rs <0.3 cm2 is sufficient

• Pad size 4 mm x 0.5 mm

• 15 round Cu wires

• Rsheet Al = 10 m/sq. ~ 18 µm


220 240 260 280 3000.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

r s [

cm

2]

Wire diameter [µm]

2 Pads

3 Pads

4 Pads

5 Pads

6 Pads

Continuous

Aluminium Rear Side

17


*TinPad by Schmid Group

TinPad*

Sn pads instead of Ag pads

Full area Al BSF

Stringed rear side


Aluminium Rear Side

17


*TinPad by Schmid Group

220 240 260 280 3000.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

r s [

cm

2]

Wire diameter [µm]

2 Pads

3 Pads

4 Pads

5 Pads

6 Pads

Continuous

Stringed rear side TinPad*

Sn pads instead of Ag pads

Full area Al BSF


Experiment

Process Flow Solar Cell Level

Alkaline texture

Emitter etch back 110 Ohm/sq.

POCl3 emitter diffusion 55 Ohm/sq.

Inkjet masking

Cz-Si, 6 inch, 2 Ohmcm

Chemical edge isolation

SiNx:H deposition

Screen printing full area Al BSF

Screen printing front side

Co-firing

3 busbars + fingers Front pads + fingers

3 busbars + fingers Front pads + fingers

IV measurement

18

Finger width 70 µm

Spacing 2.1 mm

Finger width 50 µm

Spacing 1.8 mm

Pads 500 x 700 µm2


Experiment

Process Flow Module Level

19

Stringing front- / rear side

IV measurement

Collector ribbons

Lamination process

TinPad

3 ribbons 15 wires


Experiment

Process Flow Module Level

V,I

V,I

V,I

V,I

European Solar Test Installation

in Ispra, Italy

19

Stringing front- / rear side

Aperture area - IV measurement

Collector ribbons

Lamination process

TinPad

3 ribbons 15 wires

Independently measured @


Experiment: IV Results

Design Ag [mg] Voc [mV] jsc [mA/cm²] FF [%] rs [Ωcm2] η [%]

3BB 140 640 38.1 80.0 0.41 19.45

MBB 68 640 37.7 80.2 0.32 19.34

Delta -72 0 -0.4 +0.2 -0.09 -0.11

Average IV Parameters of 3x Solar Cells

20

• Ag paste reduction >50% for multi-busbar cells (72 mg)

• jsc loss -0.4 mA/cm²

• Efficiency loss -0.11%

Similar η on cell level


Experiment: IV Results

Average IV Parameters of 3x Solar Cells and 3x 1-Cell Modules

20


3BB 140 638 37.1 76.7 1.19 18.16*

MBB 68 637 37.3 77.9 0.96 18.49*

Delta -72 -1 +0.2 +1.2 -0.23 +0.33

High module efficiencies with

multi-busbar design

*aperture area


3BB 140 640 38.1 80.0 0.41 19.45

MBB 68 640 37.7 80.2 0.32 19.34

Delta -72 0 -0.4 +0.2 -0.09 -0.11


• Multiple busbars can boost module efficiency

• Technology has high potential for metal reduction

• Ag reduction via fine line printing 72 mg 50%abs

• Module efficiencies 18.16% 3BB 18.49% MBB

• Best multi-busbar module efficiency 18.57%

• Outlook:

- Optimized front pad design increased jsc

η 18.7% possible (Simulation)

Conclusion

Advantages of Multi-Busbar Solar Cell Design

21


Thank you for your attention!

Special thanks to: Schmid Group for funding

Harald Müllejans, Diego Pavanello, Elena Salis, Roberto Galleano for IV measurements

Documents

The Multi-Busbar Design: an · PDF file4th thMetallization Workshop, May 8 2013, Konstanz S. Braun The Multi-Busbar Design: an Overview Stefan Braun1,Giso Hahn1 Robin Nissler2, Christoph